1. Field of the Invention
The present invention relates to a magnetic recording medium in which information is recorded with the direction of its magnetization and a magnetic recording apparatus for recording information in the magnetic recording medium.
2. Description of the Related Art
A magnetic recording apparatus represented by a magnetic disc drive has been well known and this magnetic recording apparatus is used as an outside recording apparatus of a computer or the like.
With development of information processing technology in recent years, demand for a magnetic recording apparatus and a magnetic recording medium having a higher recording density has been increasing. One of characteristics required for the magnetic recording medium, which satisfies such a demand is that the S/Nm (ratio between output and medium noise) is high. Various kinds of technologies have been proposed to realize this characteristic.
One of technical aims to raise the S/Nm is to improve resolution of a recording/reproducing signal and the resolution of the recording/reproducing signal is improved more as the pulse width Pw50 of a recording/reproducing waveform decreases. It is well known that the pulse width Pw50 of the recording/reproducing waveform has a relation of:
xe2x80x83axe2x88x9d(txc3x97Mr/Hc)
Pw50={square root over ( )}{2(a+d)2+(a/2)2}
where coercive force, which is magnetostatic characteristic of the magnetic recording medium, is Hc, remnant magnetization is Mr and magnetic film thickness is t. d indicates magnetic spacing.
From the above-described relation, it is considered effective to reduce the magnetic layer thickness t and increase coercive force Hc in order to improve resolution of the recording/reproducing signal. However, if the magnetic layer thickness t is reduced more than a certain level, the coercive force Hc drops, so that the resolution of the recording/reproducing signal is decreased conversely. Although technology of adding Pt to the magnetic layer of CoCr alloy has been generally adopted in order to increase the coercive force Hc, no sufficiently high resolution or S/Nm has been obtained.
Another technical object for intensifying the S/Nm is to reduce noise in medium. This noise in medium is reduced by equalizing magnetic particles in the magnetic layer by minimizing them, and by weakening magnetic reaction between magnetic particles.
As technology for weakening magnetic reaction between magnetic particles, technology of increasing composition ratio of Cr in magnetic layer of CoCr alloy has been proposed. As technology for minimizing the magnetic particle, technology of adding Ta, Nb, B, P and the like to the magnetic layer of CoCr alloy has been proposed. However, currently, noise in medium has not been reduced sufficiently.
Further, as technology for equalizing the magnetic particles while minimizing, technology of thinning a foundation layer, which is a foundation of the magnetic layer, has been also proposed. However, if the foundation layer is thinned, crystal orientation of the foundation layer is worsened and accompanied thereby, in-plane orientation of the magnetic layer is also worsened thereby leading to increase of noise in medium.
Although various kinds of technologies have been proposed, no sufficiently high S/Nm has been achieved yet with only those conventional technologies, and therefore, it is demanded to raise the S/Nm further.
Accordingly, in views of the above-described problems, an object of the present invention is to provide a magnetic recording medium and a magnetic recording apparatus capable of improving the S/Nm.
To achieve the above object, according to an aspect of the present invention, there is provided a magnetic recording medium comprising:
a base body composed of nonmagnetic metallic material;
a first foundation layer made of alloy material which is formed on the base body and composed of mainly Cr with added B;
a second foundation layer made of alloy material which is composed of one or more layers formed on the first foundation layer and in which one or more elements selected from a group consisting of Mo, Ta, Ti, W and V are mixed in Cr; and
a magnetic layer made of alloy material which is formed on the second foundation layer and composed of mainly Co.
In the magnetic recording medium of the present invention, the first foundation layer improves crystal orientation and the second foundation layer interconnects between the first foundation layer and the magnetic layer each having a different gap between the atoms. Therefore, the S/Nm is improved further.
Preferably, when a combination of composition B expressed by atomic % and thickness is expressed by a coordinate point (composition B, layer thickness), the first foundation layer has composition ratio and thickness expressed as a coordinate point within a region surrounded by lines gained by connecting a coordinate point (2 at %, 3 nm), a coordinate point (2.5 at % 3 nm), a coordinate point (4 at %, 7 nm), a coordinate point (4 at %, 9 nm), a coordinate point (3.5 at %, 13 nm), a coordinate point (2 at %, 14 nm), a coordinate point (0.5 at %, 13 nm), a coordinate point (0.5 at %, 6 nm), a coordinate point (1 at %, 4 nm) and a coordinate point (2 at %, 3 nm) successively. If the magnetic recording medium of the present invention has such atomic % and thickness, a sufficiently high S/Nm can be achieved.
Preferably, the first foundation layer contains B of 1% or more to 2.5% or less in terms of composition ratio expressed in atom quantity ratio and a thickness of 6 nm or more to 13 nm or less.
If the magnetic recording medium of the present invention has such composition ratio and thickness, not only a sufficiently high S/Nm can be achieved, but also stability of the characteristic for manufacturing error is ensured.
Preferably, the second foundation layer is made of alloy material having body-centered cubic lattice structure in which one or more elements selected from Mo, Ta, Ti, W and V are mixed in Cr at 1% or more in terms of composition ratio expressed in atom quantity ratio.
The second foundation layer having such composition and lattice structure can interconnect the first foundation layer and the magnetic layer effectively.
Preferably, the second foundation layer is comprised of plural layers and total sum of composition ratios of other elements than Cr is smaller in a layer nearer the first foundation layer, in the plural layers of the second foundation layer.
The second foundation layer comprised of plural layers can interconnect the first foundation layer and the magnetic layer effectively.
Preferably, the magnetic layer is comprised of plural layers and a magnetic layer located at the lowest level of the plural magnetic layers is an intermediate layer having a thickness of 1 nm or more to 5 nm or less and coercive force of 2,000/(4xcfx80) (kA/m) or less.
Because such an intermediate layer is possessed, the magnetic recording medium of the present invention can improve its S/Nm ratio further.
Preferably, the magnetic recording medium of the present invention further comprises a protective layer which is formed on said magnetic layer and composed of mainly C.
Because such a protective layer is possessed, in the magnetic recording medium of the present invention, its magnetic layer can be protected and a high S/Nm can be maintained for a long term.
To achieve the above-described object, according to another aspect of the present invention, there is provided a magnetic recording apparatus containing a magnetic recording medium for recording information with the direction of magnetization and a magnetic head disposed adjacent or in contact with the magnetic recording medium for indicating the magnitude of resistance depending on the direction of magnetization at each point on the magnetic recording medium so as to reproduce information by detecting the direction of magnetization at each point on the magnetic recording medium by detecting the magnitude of resistance of the magnetic head, wherein the magnetic recording medium comprises:
a base body composed of nonmagnetic metallic material;
a first foundation layer made of alloy material which is formed on the base body and composed of mainly Cr with added B;
a second foundation layer made of alloy material which is composed of one or more layers formed on the first foundation layer and in which one or more elements selected from a group consisting of Mo, Ta, Ti, W and V are mixed in Cr; and
a magnetic layer made of alloy material which is formed on the second foundation layer and composed of mainly Co.
The magnetic recording apparatus of the present invention comprises the magnetic head utilizing so-called magnetic resistance effect and the magnetic recording medium having the above-described structure so as to reproduce information at a high S/Nm.
Although only the basic configuration of the magnetic recording apparatus of the present invention is indicated in this specification, this intends to just avoid duplication and the magnetic recording apparatus of the present invention includes not only the magnetic recording apparatus of such basic configuration but also various types of the magnetic recording apparatuses corresponding to each configuration of the above-described magnetic recording medium.